1. Field of the Invention
This invention relates generally to the cultivation of plants under artificial light, and pertains more particularly to a commercially feasible method and apparatus for efficiently and effectively extracting a substantial proportion of the unwanted radiation and heat generated by the lamps providing the artificial light before it is transmitted into the growth chamber containing the plants.
2. Description of the Prior Art
In growing plants under artificial light, whether the culture be with soil or without soil, various factors must be favorable in order to encourage plant growth. Obviously, the supply of nutrients can be fairly accurately controlled, particularly where the culture is soilless, that is, where the plants are grown hydroponically. Light conditions, of course, must be favorable. While cultivating plants under artificial light can achieve a better control of the light to which the plants are subjected, nonetheless the artifical light can adversely affect the temperature of the plants, thereby interfering with their proper growth.
Hence, light and temperature are interrelated, for if the amount of artificial light is increased appreciably in a growth chamber, then the temperature of the chamber will increase accordingly due to the greater heat from the lamps. By the same token, if the light is decreased, then the resulting temperature is lowered, but there is, quite obviously, less light made available for growing the plants with a concomitant retardation of plant growth.
Too high a temperature is injurious to most plants, resulting in morphological disorders and/or reduced growing rates, so when too much heat is generated by the lamps supplying the artifical light, it becomes necessary to air condition the air in order to lower the temperature. The dehumidification resulting from the air conditioning even further reduces the growth performance of many plants. Furthermore, air conditioning is quite costly.
Consequently, a delicate balancing of the proper amount of moisture, light, air and nutrients becomes quite critical. In a hydroponic installation, other than the nutrient factor, these variables are not susceptible to precise individual control, for changing one affects the others.
An excellent approach to the problem is evidenced in U.S. Pat. No. 3,869,605 granted to Noel Davis on Mar. 4, 1975 for "Environmental Growth Control Apparatus." This patent takes into account that substantially all lamps having a high light output in the optimum wavelength range of from 400 to 700 nanometers generate substantial quantities of heat not only in the alluded to range but in other ranges as well, particularly in the infrared portion of the spectrum. The patent points out that heat emanating from any portion of the light falling outside the 400-700 range tends to merely raise the temperature within the growth chamber, producing additional loads on the temperature control equipment.
Accordingly, the referred to patented apparatus makes use of a light fixture employing a passage above the lamp through which water is circulated in an attempt to control the temperature and/or humidity within the growth chamber. An effort is made to realize as much light as possible from the lamps, the lower side of the passage, which is just above the lamps, having a procelainized surface so as to reflect at least some of the light downwardly. What heat that passes upwardly into the passage from the lamps in the fixture is removed by reason of the water that is caused to flow through the passage. The downwardly directed light, along with the heat associated therewith, is transmitted into the growing chamber. The heated water, through the agency of a remotely located heat exchanger, is employed to vaporize an absorption refrigerant, which may be an ammonia or lithium solution of the absorption unit, the vaporized refrigerant being used to chill a cooling fluid which is then supplied to heat exchange coils within the growth chamber.
While the light fixture disclosed in the aforesaid patent is a decided improvement over what was available prior thereto, a considerable amount of the energy is, nonetheless, conducted into the growing chamber, so there remains a substantial radiation load that must be removed via air conditioning. The more air conditioning resorted to, the greater the dehumidification, resulting in a condition adversely affecting plant growth.